1. Field of the Invention
This invention relates to external lubricant compositions for rigid vinyl polymers, and particularly for rigid polyvinyl chloride, and to polymer compositions containing such lubricants.
2. Description of the Prior Art
Rigid vinyl polymer compositions, such as polyvinyl chloride compositions, are utilized for producing a variety of structural articles such as plastic pipe, siding, containers and sheets. These rigid compositions are substantially unplasticized but generally contain a lubricant to facilitate the extrusion or other melt processing of the articles.
Lubricants for vinyl polymers are generally classified as external or internal lubricants. An external lubricant provides a lubricating layer between the plastic melt and the metal surfaces of the processing equipment. The external lubricant serves to coat the individual particles of the resin and inhibits their fusing together into a homogeneous melt. On the other hand, internal lubricants reduce the effective melt viscosity of the polymer at the processing temperatures in order to improve its flow properites during processing as well as promote fusing.
Previously suggested external lubricants for rigid vinyl polymers include paraffin oils and waxes as well as higher fatty acid amides. See, for example, U.S. Pat. No. 3,679,619 to Stapfer et al. (1972). In addition, U.S. Pat. No. 3,640,828 to Brotz et. al. (1972) discloses blends of a metal soap and/or a wax containing a metal soap and a hydrocarbon wax as lubricant for polyvinyl chloride. U.S. Pat. No. 3,979,347 to Brotz et. al. (1976) suggests the use of high molecular weight oxidized polyethylenes as lubricants for polyvinyl chloride. The use of low molecular weight polyethylenes as lubricants for plasticized polyvinyl chloride is suggested in Canadian Pat. No. 571,090 to Schule (1959). In addition, there has been previously utilized as lubricant for rigid polyvinyl chloride a blend of a 165.degree. F. paraffin wax and an oxidized low molecular polyethylene; however, the fusion and stability times for such blends are too short and the fusion torque is too high for some operations and in particular, multiscrew extrusion operations. It would be desirable if there were provided a lubricant composition which provided increased fusion and stability times with decreased torque at fusion.